1. Field of the Invention
The invention relates to the technical field of sheets of aluminum alloy of the AlMg type and, more particularly, of 5083 or 5086 alloy according to the standard EN 573-3, intended for welded constructions such as stationary or movable tanks and, in particular, road or railway tankers for solid or liquid substances.
2. Description of Related Art
To increase the mechanical strength of welded constructions while reducing their weight, it is desirable to utilize alloys having better mechanical characteristics than the 5083 or 5086 alloys currently used without adversely affecting the other properties for use such as weldability, resistance to corrosion and formability.
The two mechanical characteristics which, according to the principles of mechanical construction familiar to a skilled person, should be optimized to ensure suitable plastic behavior of the aluminum alloy structures are the elongation at break A and the ultimate tensile strength R.sub.m. In the case of AlMg alloys, these two characteristics tend to evolve in opposite directions if the composition of the alloy is modified and a compromise has to be found for each type of application. This is why, to calculate the behavior of the structures under rapid plastic deformation, for example in the event of an accident, the product A.times.R.sub.m is generally used for these alloys, since A and R.sub.m each have suitable minimum values.
The object of the present invention is therefore to improve this compromise between the elongation and the tensile strength while ensuring satisfactory corrosion resistance and a production program which is as simple and reliable as possible.
Japanese patent application JP 06-212373 gives examples of sheets of AlMgMn alloy exhibiting a good compromise between the elongation and the strength, but production by hot-rolling necessitates a minimum delivery temperature from the rolling mill of 450.degree. C., demanding a rapid production rate and minimum lubrication and not allowing reliable and economic production of strips.
Japanese patent application JP 06-93365 also provides sheets of AlMgMn alloy having mechanical characteristics satisfying the object set, but the production thereof involves a complicated, expensive program including hot-rolling followed by intermediate annealing, warm rolling and final annealing.